The present invention relates to a vacuum exhaust system for a processing apparatus.
During the process of fabricating semiconductor devices, various processing apparatuses, such as a low-pressure CVD apparatus, are used for forming films on a semiconductor wafer that is the object to be processed in an environment at a predetermined temperature, with a predetermined processing gas, and at a predetermined pressure. This type of processing apparatus is provided with a processing chamber for accommodating semiconductor wafers and causing a predetermined process to be performed thereon, and it is also provided with a vacuum exhaust system for creating a predetermined low-pressure environment within that processing chamber.
An example of a vacuum exhaust system provided in a prior-art processing apparatus is shown in FIG. 4. This vacuum exhaust system is provided with a mechanical booster pump (MBP) 42 and a pressure control valve 45, connected by a main pipeline 41 to a processing chamber 2 of a processing apparatus 1. A small-diameter roughing pipeline 47 having an auxiliary valve 46 is connected parallel to the main pipeline 41 in such a manner as to link parts thereof that are before and after a main valve 44, and also a vacuum-achieving pipeline 51 having valves 49 and 50 on either side of a turbo molecule pump (TMP) 48 is connected parallel to the main pipeline 41 in such a manner as to link parts thereof that are before the main valve 44 and after the pressure control valve 45. In FIG. 4, reference number 37 denotes a pressure sensor for determining the pressure in the processing chamber 2 and reference number 17 denotes a processing gas supply line having a switching valve 19, which supplies processing gas into the processing chamber 2 and which is connected to a source of processing gas that is not shown in the figure.
With the vacuum exhaust system of the prior-art processing apparatus 1 configured in this manner, first of all a dry pump (DP) 43 is activated in a state in which all of the valves 19, 44, 45, 46, 49, and 50 are closed. The rearward valve 50 of the vacuum-achieving pipeline 51, the auxiliary valve 46 of the roughing pipeline 47, and the pressure control valve 45 are then opened, and roughing at a low exhaust flowrate is performed in such a manner as to ensure that no condensation or dust scattering is caused by sudden changes in pressure within the processing chamber 2. Once the pressure within the processing chamber 2 has reached 10 Torr or so because of this roughing exhaust, the mechanical booster pump 42 is activated, the auxiliary valve 46 is closed, and the main valve 44 is opened, and thus the pressure within the processing chamber 2 is further reduced. Once this has reduced the pressure within the processing chamber 2 to 1 Torr or so, the turbo molecule pump 48 is activated, the main valve 44 is closed, and the forward valve 49 of the vacuum-achieving pipeline 51 is opened, and thus the degree of vacuum within the processing chamber 2 is reduced to the level of 10.sup.-6 Torr or so, causing any adhered particles of water or the like attached to the inner walls of the processing chamber 2 to be removed therefrom. The forward and rearward valves 49 and 50 are then closed, the turbo molecule pump 48 is halted, and the main valve 44 and the switching valve 19 of the processing gas supply pipe 17 are opened, and thus the processing is performed while the pressure within the processing chamber 2 is maintained at a predetermined processing pressure (between 0.1 and 50 Torr) by the pressure control valve 45.
However, the mechanical booster pump 42 used in the processing and as backup for the turbo molecule pump 48 in the above described prior-art vacuum exhaust system is arranged in a utility area that is some distance from the processing chamber 2 provided within the clean room, and thus the main pipeline 41 from the processing chamber 2 to the mechanical booster pump 42 is long (12 to 15 m). This means that the diameter of the main pipeline 41 has to be increased because the conductance of the piping system is so large, and also inevitably a pump with a large exhaust speed (exhaust flow) is necessary, which has the result of increasing the size and cost of the entire system.